The Evolution of Early-Life Effects on Social Behaviour - Why Should Social Adversity Carry Over to the Future?

Numerous studies have shown that social adversity in early life can have long-lasting negative consequences for social behaviour in adulthood, consequences that may in turn be propagated to future generations. Given these intergenerational effects, it is puzzling why natural selection might favour such sensitivity to an individuals early social environment. To address this question, we model the evolution of social sensitivity in the development of in helping behaviours, showing that natural selection indeed favours individuals whose tendency to help others is dependent on early-life social experience. We find that natural selection typically favours positive social feedbacks, in which individuals who received more help in early life are also more likely to help others in adulthood, while individuals who received no early-life help develop low tendencies to helping others later in life. This positive social sensitivity is favoured because of an intergenerational relatedness feedback: patches with many helpers tend to be more productive, leading to higher relatedness within the local group, which in turn favours higher levels of help in the next generation.